In some applications, especially in battery-powered portable devices, the only available power supply has a maximum voltage lesser than the desired peak-to-peak voltage swing of an output signal. One solution to this problem has been to use a DC-to-DC converter to boost the power supply voltage applied to the output stage of a multi-stage amplifier. However, DC-to-DC converters introduce undesirable noise to the device. Components that can eliminate such noise, and other components needed to regulate the output of such converters, require significant amount of surface area in integrated circuits and can waste power.
Typically, power obtained at an output of a headphone amplifier drives a load and is in the range of few tens of milli watts. The headphone amplifier is typically coupled between a core of a portable electronic device and the headphone. The core operates with a supply having a reference voltage different from another reference voltage of the headphone amplifier. Hence, a capacitor is used to couple the core with the headphone amplifier leading to a larger chip area and a bulkier amplifier device. Further, the capacitor modifies frequency response by reducing pass band of the headphone amplifier. The pass band reduces with the value of the capacitor causing a loss in bass in the headphone amplifier.
Conventional amplifiers use a dual voltage supply for its power supply requirements and hence an external circuit is required for generating a power rail that is negative with respect to the ground. In addition to the power rail, the external circuitry also provides noise in the form of undesired ripples. The conventional headphone amplifier requires a large Power Supply Rejection Ratio (PSRR) in order to filter the undesired ripples at the output of the conventional headphone amplifier. Further, the conventional headphone amplifier uses a Low-dropout (LDO) regulator which results in a larger consumption of area. Also, the LDO regulator contributes for a loss of power causing a rise in the total power dissipation of the conventional headphone amplifier. An offset in a conventional headphone amplifier circuit directly adds up to the quiescent current. In light of the foregoing discussion, an amplifier circuit which overcomes one or more of the above mentioned limitations is needed.